Combined Effects of Temperature and Humidity on the PDIV of Twisted Pairs

The partial discharge inception voltage (PDIV) of magnet wires depends on ambient temperature and humidity. Thus, both quantities might affect the reliability of inverter-fed wire-wound motors. Contradictory results have been reported in literature, so this paper discusses a variety of experiments aimed at explaining the dependence of PDIV on both temperature and humidity. For very high temperature and humidity levels, the results are surprising and difficult to explain. Temperature and humidity influence the air density, the dielectric permittivity, and the surface conductivity of the enamel, making very difficult to disentangle their relative contributions.